I couldn't resist getting this one to play with. Within some limits, C-mount lenses can be used on the E-P1. In general, the main concerns are physical compatibility and image circle size.

This particular lens does have an image circle smaller than the FourThirds size sensor, so the edges and corners are simply not present. Also, some physical modification is required to get it to fit and have infinity focus. More on that modification here. Also there are pics of the lens - mine will come later. I am using the same adapter as shown there, but I have not done the modification yet, so my infinity focus position is actually focusing about 30cm from the sensor plane.

The lens is fully manual. An aperture ring starts at f/1.3. The next mark is at f/2, and goes up from there to f/16 in one stop intervals before reaching a closed setting. It has three rounded aperture blades so bokeh could be interesting when stopped down. The focus ring goes from infinity with the closest mark at 0.4m, although it does turn a bit past that. The front does rotate with focus so care needs to be taken if you intend to use a polarising filter. There are no detents on either aperture or focus rings so they can be continuously adjusted.

A quick FoV test at different apertures with the Computar:

f/1.3

f/5.6

f/16

I used the E-P1 in aperture priority mode fixed in ISO200. The E-P1 metering doesn't seem to work quite right, as the image gets dimmer as you stop down. For whatever reason it doesn't seem to be compensating adequately for this. In the samples before, I did adjust the levels to compensate for this. Note the red dot is not round at f/5.6. The border region changes characteristic too. Also notice there is some barrel distortion from the lens. I think the bokeh at f/1.3 is quite decent, even if there is a bit of a highlight to it.

Subjectively it is a bit soft wide open, but sharpens quickly stopped down a little.

So how does the FoV compare to existing lenses like the Olympus kit zoom at 14mm, and the Panasonic 20mm f/1.7?

Olympus 14-42 at 14mm f/3.5

Panasonic 20mm f/3.5

Quite obviously as the focal length increases, you lose FoV. To help show this, I have tried to place boxes showing the approximate area compared to the Computar. This isn't exact I think due to the distortion.

I'm not sure why the Oly is off center compared to the others... I didn't intentionally move the tripod between tests.

Next step: do the infinity focus modification then take some serious shots with it.

I just spent an hour or so taking off the metal to get a better fit into the adapter. I still don't get infinity focus, but I don't think I can get it in further without totally ruining the mount as I don't think there's much metal left. Maximum focus distance is now about 1m.

Also, I should add all the earlier test shots were taken with a protection filter on the lens. This came with it so I left it. I have now took it off, and it seems to have made the image circle a little bit bigger.

Quick aspect ratio test.

4:3 f/2.8

16:9 f/2.8

I didn't bother uploading the 3:2 image - as the camera just does a crop it's somewhere between the above. Both are more or less at minimum focus distance.

I also think I found a way around the exposure problem I saw earlier. I had it on whole scene metering, and the dark corners must have been throwing it off. Changed to center weighted and its behaving much better now.

The lens does suffer a bit from flare from out of shot light sources.

Sharpness at f/2.8 is nice and sharp. I'm undecided on f/1.3 as it's quite difficult to be sure of focus even with zoomed live view. I think I might have my first "soft focus" lens as so far it feels soft, but not in a bad way if that makes sense.

Now, looking forward the lack of infinity focus does put a crimp on my original intention, which was to use this for wide angle astrophotography. I can kinda get infinity focus by going hyperfocal, but that's at such a small aperture I might as well stick with the kit zoom.

I haven't been this excited in a lens in a while... but I just found out on a search how to get infinity focus that the earlier mount modification didn't quite get me. There's screws under the focus rubber ring that adjusts the focus range of the lens, and there's enough overshoot in the system to reach infinity. Done a proof of concept mod to check it works, I need to fine tune that adjustment then I'm done

Done the modification now... there's 4 screws under the focus ring rubber strip. One is the infinity stop. Removing that lets it go past infinity mark and I used this to test it out initially. The other three screws couple the ring to the internal mechanism. So loosening them lets you reset the position of the focus ring to actual focus distance. A little trial and error later I got infinity-ish at infinity

In a quick test, wide open performance isn't great. It's definitely soft with what I guess is uncorrected spherical aberration. It never gets to a point. If you get the bright part as small as you can, there is still a lighter disc around it. This pretty much rules out its use for serious astrophotography, but might still be fun for big sky stuff.

Distortion isn't great either. Initially I thought it had barrel distortion, but checking the corners I think it is moustache shaped.

I don't have any samples really worth posting right now.

This is a test in my kitchen. There is no significant light on in the kitchen. Only a small bit of spillage from the next room and outside. 1 second exposure hand held helps pull any light in there, combined with the f/1.3. The wide angle and body IS combine to allow longer hand held shots. I'm getting about 50% acceptably sharp shots at 1 second but I am out of practice...

Took it for a test down the park yesterday... following are the initial impressions:

Centre sharpness great from wide open, although at f/1.3 it suffers from reduced contrast. This clears up from f/2.
Sharpness degrades as you go away from the centre, but this does improve a lot as you stop down. The extreme border does remain soft regrdless.

The lens exhibits blue/yellow lateral CA which is noticeable. I haven't observed any noticeable longitudinal CA so far.

Vignetting... the image circle doesn't fill the m4/3 sensor. It does expand slightly as you stop down.

The three aperture blades do give triangular bokeh which gives its own character.

As is, the lens doesn't do macro with a minimum focus distance around 40cm for not much magnification at all.

Distortion... in field conditions it seems to look like some barrel distortion at longer distances, noticeable on straight lines e.g. buildings. At close focus there was a hint of moustache. This really needs a test chart to nail.

Example of vignetting varying with aperture (also shows distortion):

f/1.3

f/2.8

f/8

100% lossless crops from camera jpegs as above, centre and top right corner of building.

f/1.3 (note this was a bit over exposed as the camera ran out of headroom)

f/2.8

f/8 looks like diffraction has softened the centre slightly, but stopping down helps in the corner.

And finally, some flare example. Sun was out of shot to top left corner. The lens might be helped with a suitable hood.

f/1.3

f/5.6

f/16

f/1.3

Because of the lack of coverage, it isn't really wider than the kit zoom at 14mm, but of course you do gain a lot of aperture should you need it. I think that is the strength of the lens.

Now for more samples, having a close look at close up performance.

This is what it looks like with the bluebells at minimum focus distance. Not really close at all with the wide angle. How's the bokeh?

We're still at f/1.3 here. It's nice and round wide open in the middle, with a bit of outline. The shape does degrade at the edges (taken from top-right). The CA also impacts here. I haven't tried correcting it yet.

If you want to do really close ups, you need external help. Here I'm using part of a two piece "wide angle adapter". One piece by itself works as a close up filter. It appears to be somewhat corrected and coated, but still may impact lens performance. This lets you get pretty close. I estimate the maximum magnification to be around 0.2x.

I like this one personally. This was stopped down a bit as you can see from the triangular bokeh which in this shot I think adds to not detracts from the overall impact.

I think I'm going to like exploring semi-macro wide angle. The DoF fall off is much less steep than with longer focal lengths, so even slightly out of focus areas are usable. Also the wide perspective background will be interesting. I always wanted a wide angle macro, this combination is a good start to it.